attending the Efjlux of condensed Air and Steam. 33S 



overheated state of that part of the boiler which contains the 

 steam, is one, at least, of the causes which induce the effect. 

 It will be readily perceived, that by closing the door of the 

 stove a considerable increase of temperature would be occa- 

 sioned in the upper part of the boiler where the steam was 

 lodged, and I found that in almost every instance in which this 

 was done, the negative electricity of the boiler, and the ^05/- 

 tive electricity of the steam, began to decline, and continued 

 so to do until they vanished entirely, and then positive elec- 

 tricity gradually appeared in the boiler, and negative electri- 

 city in the emitted steam. A diminished state of the water in 

 the boiler would also, of course, favour the accumulation of 

 heat in the higher region of the boiler, and such a state of the 

 water proved to be likewise conducive to the conversion of the 

 electricities. I have reason, however, to think that there are 

 other causes by which a change is effected in the electrical 

 states of the boiler and steam-cloud ; but before any definite 

 opinion can be formed on this point, I consider further ex- 

 periments to be necessary. 



I shall now speak of the effects of pressure, first, when the 

 steam-cloud evolves positive electricity, and secondly, when 

 it liberates negative electricity. 



In experiments to ascertain the comparative intensity of 

 the electricity evolved by steam at different pressures, it is of 

 course essential that equal iveig/its of steam, and not equal 

 volumes, should be emitted in equal times; and to effect this 

 condition it is necessary that the discharging aperture should 

 be diminished in the same proportion that the pressure is in- 

 creased, and vice versa. The safety-valve is in this respect 

 a self-regulating apparatus, because it permits an escape of 

 steam precisely equal to the production, which, with a uni- 

 form fire, is the same at all pressures. Another requisite in 

 such experiments is, that the steam should issue in states of 

 equal dryness. If a strong fire be used, the discharfie at low 

 pressures is so voluminous, that it is exceedingly apt to sweep 

 unvaporized water out of the boiler, and thereby to dissipate 

 the electricity, or conduct it to the valve. 



By availing myself, then, of the safety-valve as a means of 

 equalizing the escape, and by maintaining the fire at once 

 uniform and moderate, I was enabled to effectuate equal emis- 

 sions of dry steam, under successive augmentations of press- 

 ure, and the following are the results I obtained, so far as 

 they apply to the usual condition of the steam-cloud, or that 

 in which it evolves positive electricity. 



In the first place I removed the valve from its seat, and 

 suffered the steam to escape without any restraint whaterer j 



